equip it with 1 "Destruction Sword" monster from your GY
The NPC you need to defeat is the Sector Security and he didn't show up for us until Stage 3 so be sure to get it up there before trying
Cheerios, Stef Hey
Ive also heard of people including their custom designed cards in Cube, which sounds like one of the best places for it
Barry, Cheren, Tierno, Hau, Hop, and Nemona (all rivals from their respective games) just draw 3 cards with no additional effect, while others have extra effects on top of the 3-card draw, such as Bird Keeper switching the player's active Pokmon
This makes some amount of sense, given Mitsurugi can afford the hefty Extra Deck payment, but I would wonder if targeting protection from opposing duelists could cause it to lose what little favor it has